19-1896; Rev 0; 1/01 256-Tap, µPoT, Low-Drift, Digital Potentiometer The MAX5402 serves well in applications requiring digitally controlled resistors, including adjustable voltage references and programmable gain amplifiers (PGAs). A nominal end-to-end resistor temperature coefficient of 35ppm/°C makes this part suitable for use as a variable resistor in applications such as low-tempco adjustable gain and other circuit configurations. This device is guaranteed over the extended industrial temperature range (-40°C to +85°C). Features ♦ Small Footprint, 8-Pin µMAX Package ♦ Ultra-Low 100nA Supply Current ♦ +2.7V to +5.5V Single-Supply Operation ♦ 256 Tap Positions ♦ Low Ratiometric Temperature Coefficient 5ppm/°C ♦ Low End-to-End Resistor Temperature Coefficient 35ppm/°C ♦ Power-On Reset: Wiper Goes to Midscale (Position 128) ♦ Glitchless Switching Between the Resistor Taps ♦ 3-Wire SPI™-Interface Compatible ♦ 10kΩ Resistor Value Ordering Information ________________________Applications Mechanical Potentiometer Replacement TEMP. RANGE PART Low-Drift PGAs Adjustable Voltage References MAX5402EUA -40°C to +85°C PINPACKAGE 8 µMAX R (kΩ) 10 µPoT is a trademark of Maxim Integrated Products. SPI is a trademark of Motorola, Inc. Functional Diagram Pin Configuration VDD TOP VIEW H R 8 DIN 8-BIT SHIFT REGISTER R 8-BIT LATCH 8 256 DECODE W L L 1 8 H GND 2 7 W 3 6 VDD DIN 4 5 SCLK MAX5402 CS MAX5402 SCLK CS POR CLOCK LOGIC µMAX GND ________________________________________________________________ Maxim Integrated Products 1 For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX5402 General Description The MAX5402 µPoT™ digital potentiometer is a 256-tap variable resistor with 10kΩ total resistance in a tiny 8pin µMAX package. This device functions as a mechanical potentiometer, consisting of a fixed resistor string with a digitally controlled wiper contact. It operates from +2.7V to +5.5V single-supply voltages and uses an ultra-low 0.1µA supply current. This device also provides glitchless switching between resistor taps, as well as a convenient power-on reset (POR) that sets the wiper to the midscale position at power-up. A low 5ppm/°C ratiometric temperature coefficient makes it ideal for applications requiring low drift. MAX5402 256-Tap, µPoT, Low-Drift, Digital Potentiometer ABSOLUTE MAXIMUM RATINGS VDD to GND ..............................................................-0.3V to +6V DIN, SCLK, CS to GND ............................................-0.3V to +6V H, L, W to GND .............................................-0.3V to (VDD + 0.3) Maximum Continuous Current into Pins H, L, and W ...........1mA Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.1mW/°C above +70°C) ............330mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VDD = +5V, VH = VDD, VL = 0, TA = TMIN to TMAX. Typical values are at VDD = +5V, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC PERFORMANCE (Voltage-Divider Mode) Resolution N 8 Bits Integral Nonlinearity (Notes 1, 2) INL ±1/2 LSB Differential Nonlinearity (Notes 1, 2) DNL ±1 LSB End-to-End Resistor Tempco TCR 35 ppm/°C 5 ppm/°C Full-Scale Error -6 LSB Zero-Scale Error +6 LSB Ratiometric Resistor Tempco DC PERFORMANCE (Variable-Resistor Mode) Resolution Integral Nonlinearity (Notes 1, 3) Differential Nonlinearity (Notes 1, 3) N INL DNL 8 Bits VDD = +5V ±1 VDD = +3V ±3 LSB VDD = +5V ±1/2 LSB VDD = +3V ±1/2 LSB LSB DC PERFORMANCE (Resistor Characteristics) Wiper Resistance (Note 4) RW Wiper Capacitance CW End-to-End Resistance RHL VDD = +5V 275 VDD = +3V 550 46 7.5 10 Ω pF 12.5 kΩ DIGITAL INPUTS Input High Voltage VIH Input Low Voltage VIL 0.7 ✕ VDD V 0.3 ✕ VDD ±1.0 Input Leakage Current Input Capacitance V µA 5 pF 100 ns TIMING CHARACTERISTICS (ANALOG) Wiper-Settling Time tS To 50% of final value from code 0 to code 128 TIMING CHARACTERISTICS (DIGITAL) (Note 5) (Figure 2) SCLK Clock Period tCP 100 ns SCLK Pulse Width High tCH 40 ns 2 _______________________________________________________________________________________ 256-Tap, µPoT, Low-Drift, Digital Potentiometer (VDD = +5V, VH = VDD, VL = 0, TA = TMIN to TMAX. Typical values are at VDD = +5V, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SCLK Pulse Width Low tCL 40 CS Fall to SCLK Rise Setup Time tCSS 40 ns ns SCLK Rise to CS Rise Hold Time tCSH 0 ns DIN Setup Time tDS 40 ns DIN Hold Time tDH 0 ns SCLK Rise to CS Fall Delay tCS0 10 ns CS Rise to SCLK Rise Hold tCS1 40 ns CS Pulse Width High tCSW 100 ns Supply Voltage VDD 2.7 Supply Current IDD POWER SUPPLIES CS = SCLK = DIN = VDD VDD = +5V 0.8 VDD = +2.7V 0.1 5.5 V 5 µA µA Note 1: Linearity is defined in terms of the H-to-L code-dependent resistance. Note 2: The DNL and INL are measured with the potentiometer configured as a voltage-divider with H = VDD and L = 0. The wiper terminal is unloaded and measured with an ideal voltmeter. Note 3: The DNL and INL are measured with the potentiometer configured as a variable resistor. H is unconnected and L = 0. The wiper terminal is driven with a source current of 200µA at VDD = +3V and 400µA at VDD = +5V. Note 4: The wiper resistance is the worst value measured, injecting a current, IW = VDD/RHL into terminal W. Note 5: Digital timing is guaranteed by design. ________________________________________________________________________________________ 3 MAX5402 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) END-TO-END RESISTANCE % CHANGE vs. TEMPERATURE WIPER RESISTANCE vs. WIPER VOLTAGE 250 VDD = +3V 225 200 MAX5402 Toc02 0.00 -0.05 VDD = +5V 175 -0.10 150 -0.15 125 -0.20 100 0 1 2 3 4 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 5 WIPER VOLTAGE (V) TEMPERATURE (°C) RESISTANCE vs. INPUT CODE VARIABLE RESISTOR DNL vs. INPUT CODE 0.25 MAX5402 Toc03 10 9 8 0.20 0.15 7 RDNL (LSB) W-TO-L RESISTANCE (kΩ) 0.05 6 5 4 MAX5402 Toc04 WIPER RESISTANCE (Ω) 275 0.10 END-TO-END RESISTANCE % CHANGE MAX5402 Toc01 300 0.10 0.05 0.00 -0.05 3 2 -0.10 1 -0.15 0 -0.20 0 32 64 96 128 160 192 224 256 0 32 INPUT CODE (DECIMAL) 128 160 192 224 256 VOLTAGE-DIVIDER DNL vs. INPUT CODE MAX5402 Toc06 0.2 96 0.08 MAX5402 Toc05 0.3 64 INPUT CODE (DECIMAL) VARIABLE RESISTOR INL vs. INPUT CODE 0.06 0.04 DNL (LSB) 0.1 RINL (LSB) MAX5402 256-Tap, µPoT, Low-Drift, Digital Potentiometer 0.0 -0.1 0.00 -0.02 -0.2 -0.04 -0.3 -0.06 -0.08 -0.4 0 32 64 96 128 160 192 224 256 INPUT CODE (DECIMAL) 4 0.02 0 32 64 96 128 160 192 224 256 INPUT CODE (DECIMAL) _______________________________________________________________________________________ 256-Tap, µPoT, Low-Drift, Digital Potentiometer VOLTAGE-DIVIDER INL vs. INPUT CODE SUPPLY CURRENT vs. TEMPERATURE 1.0 SUPPLY CURRENT (µA) 0.10 0.05 0.00 -0.05 -0.10 MAX5402 Toc08 0.15 INL (LSB) 1.2 MAX5402 Toc07 0.20 VDD = +5V 0.8 0.6 0.4 0.2 -0.15 VDD = +3V -0.20 0.0 0 32 64 96 128 160 192 224 256 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 INPUT CODE (DECIMAL) TEMPERATURE (°C) INPUT LOGIC VOLTAGE TAP-TO-TAP SWITCHING TRANSIENT MAX5402 toc09 MAX5402 Toc10 10 +2.51V +2.49V +5V CS 0 SUPPLY CURRENT (mA) 1 VW-L 0.1 VDD = +5V 0.01 0.001 VDD = +3V 0.0001 200ns/div (CODE 127 TO 128) 0 1 2 3 4 5 DIGITAL INPUT VOLTAGE (V) Pin Description PIN NAME FUNCTION 1 L 2 GND Low Terminal of Resistor 3 CS Chip Select Input 4 DIN Serial Data Input 5 SCLK 6 VDD 7 W Wiper Terminal 8 H High Terminal of Resistor Ground Serial Clock Input Power Supply. Bypass with a 0.1µF capacitor to GND. ________________________________________________________________________________________ 5 MAX5402 Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX5402 256-Tap, µPoT, Low-Drift, Digital Potentiometer POT REGISTER LOADED CS SCLK 8TH CLOCK PULSE 1ST CLOCK PULSE DIN D7 D6 D5 D4 D3 D2 D1 D0 LSB MSB TIME Figure 1. Serial Interface Timing Diagram CS tCSW tCSO tCS1 tCSS tCL tCH tCP tCSH SCLK tDS tDH DIN Figure 2. Detailed Serial Interface Timing Diagram Detailed Description The MAX5402 consists of 255 fixed resistors in series between pins H and L. The potentiometer wiper (pin W) can be programmed to access any one of the 256 different tap points on the resistor string. The MAX5402 has an SPI-compatible 3-wire serial data interface to control the wiper tap position. This write-only interface contains three inputs: Chip Select (CS), Data In (DIN), and Data Clock (SCLK). When CS is taken low, data from the DIN pin is synchronously loaded into the 8-bit serial shift register on the rising edge of each SCLK pulse (Figure 1). The MSB is shifted in first, as shown in Figure 3. Note that if CS is not kept low during the entire data stream, the data will be corrupted and the device 6 will need to be reloaded. After all 8 data bits have been loaded into the shift register, they are latched into the decoder once CS is taken high. The decoder switches the potentiometer wiper to the tap position that corresponds to the 8-bit input data. Each resistor cell is 10kΩ/255 or 39.2Ω for the MAX5402. The MAX5402 features POR circuitry. This sets the wiper to the midscale position at power-up by loading a binary value of 128 into the 8-bit latch. The MAX5402 can be used as a variable resistor by connecting pin W to either pin H or L. _______________________________________________________________________________________ 256-Tap, µPoT, Low-Drift, Digital Potentiometer B1 (D6) B2 (D5) B3 (D4) B4 (D3) B5 (D2) B6 (D1) MAX5402 Data Word B0 (D7) B7 (D0) (MSB) First Bit In (LSB) Last Bit In Figure 3. Serial Data Format Applications Information The MAX5402 is intended for a variety of circuits where accurate, fine-tuned adjustable resistance is required, such as in adjustable voltage or adjustable gain circuit configurations. The MAX5402 is used in either a potentiometer divider or a variable resistor configuration. R3 H +5V MAX5402 R1 Adjustable Current to Voltage Converter R2 W Figure 4 shows the MAX5402 used with a MAX4250 low-noise op amp to precisely tune a current-to-voltage converter. Pins H and W of the MAX5402 are connected to the node between R3 and R2, and pin L is connected to ground. L VO MAX4250 Adjustable Gain Amplifier The MAX5402 is used again with the MAX4250 to make a digitally adjustable gain circuit as shown in Figure 5. The normal feedback resistor is replaced with the MAX5402 in a variable resistor configuration, so that the gain of the circuit can be digitally controlled. VO / IS = R3(1 + R2 / R1) + R2 Figure 4. I to V Converter Adjustable Voltage Reference In Figure 6, the MAX5402 is shown with the MAX6160 to make an adjustable voltage reference. In this circuit, the H pin of the MAX5402 is connected to the OUT pin of the MAX6160, the L pin of the MAX5402 is connected to GND, and the W pin of the MAX5402 is connected to the ADJ pin of the MAX6160. The MAX5402 allows precise tuning of the voltage reference output. A low 5ppm/°C ratiometric tempco allows a very stable adjustable voltage overtemperature. +5V VS VO MAX4250 L R2 H MAX5402 R1 W VO / VS = 1 + R2 / R1 Figure 5. Noninverting Amplifier ________________________________________________________________________________________ 7 256-Tap, µPoT, Low-Drift, Digital Potentiometer MAX5402 Chip Information +5V TRANSISTOR COUNT: 3475 PROCESS: BiCMOS VIN VO REF OUT H MAX6160 ADJ W GND VO = MAX5402 L 1.23V ✕ 255 C WHERE C IS THE DECIMAL EQUIVALENT WRITTEN CODE. Figure 6. Adjustable Voltage Reference 8 _______________________________________________________________________________________ 256-Tap, µPoT, Low-Drift, Digital Potentiometer 8LUMAXD.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX5402 Package Information